The present invention relates to an exhaust gas vent valve for an exhaust gas driven turbocharger.
With the exhaust gas driven turbochargers mounted on the internal combustion engines of automobiles, construction machines or the like, the exhaust gases from the engine drives a turbine which in turn drives the blower of a compressor disposed in coaxial relationship with the turbine so as to increase the pressure and weight of air to be charged into the engine, thereby attaining high outputs or speeds. Because such turbochargers are driven by the exhaust gases, the rotational speed of the turbine varies linearly with the engine speed; that is, the flow rate of the exhaust gases. For instance, as the speed of the engine increases, the discharge rate of exhaust gases increases and consequently the rotational speed of the turbine rises so that the pressure of air charged into the engine exceeds a predetermined level. When the air under abnormally high pressures is charged into the engine, the combustion pressures increase, resulting in damages to cylinders and a connecting rod. In order to overcome these problems, the turbochargers are in general equipped with an exhaust gas vent valve for controlling the flow rate of the exhaust gases flowing from the exhaust manifold of the engine into the turbine so that the discharge pressure of the compressor will not exceed a predetermined level. Especially the exhaust gas driven turbochargers are equipped with the exhaust gas vent valve of the type described above in order to improve the torque characteristics of the engine.
In FIG. 1 is shown a conventional exhaust gas driven turbocharger 2. The exhaust gases from an internal combustion engine 1 flow through an engine exhaust pipe 4 into a turbine wheel chamber 3 so as to drive a turbine wheel 5 and is discharged through a turbine exhaust pipe 6 to the surrounding atmosphere. As the turbine wheel 5 is driven, a blower wheel 7 of a compressor 8 which is also carried by the shaft of the turbine wheel 5 is rotated and the pressurized air flows from an outlet port 9 through an induction pipe 10 into the engine 1.
As described above, an exhaust gas vent valve 11 has a function of controlling the pressure of air to be charged into the engine 1 by the compressor 8 so as to prevent the air pressure from rising above a predetermined level. To this end, a bypass pipe 12 is provided to connect the engine exhaust pipe 4 with the turbine exhaust pipe 6 through the exhaust gas vent valve 11. An exhaust gas passage 15 having an inlet 13 and an outlet 14 is formed in the exhaust gas vent valve 11 and communicates with the bypass line 12. A valve body 16 is disposed at the inlet 13 so as to open and close the exhaust gas passage 15.
The exhaust gas vent valve 11 has a diaphragm housing 19 which is divided by a diaphragm 18 into a pressure chamber 20 and an atmospheric pressure chamber 21. The valve stem 17 of the valve body 16 is connected to the diaphragm 18. The pressure chamber 20 communicates through an inlet port 22 and a pipe line with the air induction pipe 10 so that the pressure at the discharge port 9 of the compressor 8 may be transmitted into the pressure chamber 20. The atmospheric pressure chamber 21 communicates through ports with the surrounding atmosphere, and a coiled spring 23 is loaded in the atmospheric pressure chamber 21 between the end wall thereof and the diaphragm 18. The force or spring constant of the coiled spring 23 is so selected that unless the pressure at the discharge port 9 of the compressor 8 exceeds a predetermined level the diaphragm 18 will not be permitted to deflect itself toward the atmospheric pressure chamber 21. That is, as far as the discharge pressure of the compressor 8 is below a predetermined level, the diaphragm 18 remains in such a position that the valve body 16 closes the inlet 13 of the exhaust passage 15. However, when the discharge pressure exceeds a predetermined level, the diaphragm 18 is deflected toward the atmospheric pressure chamber 21 so that the valve body 16 is moved away from its seat to open the inlet 13. As a result, part of the exhaust gases may bypass the turbine wheel chamber 3 so that the rotational speed of the turbine wheel 5 drops and consequently the discharge pressure of the compressor 8 decreases.
The exhaust gas vent valve 11 is fabricated separately from the turbocharger 2 and must communicate with the engine exhaust pipe 4 and the turbine exhaust pipe 6 through the bypass pipe 12 and with the air induction pipe 10 through the pressure transmission line. That is, when the exhaust vent valve 11 is mounted on the engine 1, an additional piping system must be provided to communicate the exhaust vent valve 11 with the engine exhaust pipe 4, the turbine exhaust pipe 6 and the air induction pipe 10. As a result, the engine is inevitably increased both in weight and volume so that a large engine space is required, the outer appearance is degraded and the overall weight of an automobile or a construction machine is increased.
The present invention was made to overcome the above and other problems encountered in the prior art exhaust gas driven turbochargers.
One of the objects of the present invention is therefore to provide an exhaust gas vent valve system for controlling the flow rate of exhaust gases flowing into a turbine of an exhaust gas driven turbocharger which may be fabricated as a unitary assembly with the turbocharger or may be directly mounted on it, whereby the exhaust gas driven turbocharger may be made compact in size and light in weight.
The present invention will become apparent from the following description of one preferred embodiment thereof taken in conjunction with the accompanying drawings.